Horizontal well drilling and production have become increasingly important to the oil industry in recent years. While horizontal wells have been known for many years, only relatively recently have such wells been determined to be a cost-effective alternative to conventional vertical well drilling. Although drilling a horizontal well costs substantially more than its vertical counterpart, a horizontal well frequently improves production by a factor of five, ten or even twenty in naturally-fractured reservoirs. Generally, projected productivity from a horizontal wellbore must triple that of a vertical wellbore for horizontal drilling to be economical. This increased production minimizes the number of platforms, cutting investment and operational costs. Horizontal drilling makes reservoirs in urban areas, permafrost zones and deep offshore waters more accessible. Other applications for horizontal wellbores include periphery wells, thin reservoirs that would require too many vertical wellbores, and reservoirs with coning problems in which a horizontal wellbore could be optimally distanced from the fluid contact.
Also, some horizontal wellbores contain additional wellbores extending laterally from the primary vertical wellbores. These additional lateral wellbores are sometimes referred to as drainholes and vertical wellbores containing more than one lateral wellbore are referred to as multilateral wells. Multilateral wells are becoming increasingly important, both from the standpoint of new drilling operations and from the increasingly important standpoint of reworking existing wellbores, including remedial and stimulation work.
As a result of the foregoing increased dependence on and importance of horizontal wells, horizontal well completion, and particularly multilateral well completion, have been important concerns and continue to provide a host of difficult problems to overcome. Lateral completion, particularly at the juncture between the main and lateral wellbores, is extremely important to avoid collapse of the wellbore in unconsolidated or weakly consolidated formations. Thus, open hole completions are limited to competent rock formations; and, even then, open hole completions are inadequate since there is no control or ability to access (or reenter the lateral) or to isolate production zones within the wellbore. Coupled with this need to complete lateral wellbores is the growing desire to maintain the lateral wellbore size as close as possible to the size of the primary vertical wellbore for ease of drilling and completion. Additionally, there is substantial concern for prematurely setting the liner in the casing or inadvertently hanging the liner near the later wellbore on the casing since such actions could result in extensive and costly time delays.
Various types of liner hangers are well known in the art and have been used extensively in conventional well completions and have also been utilized in multilateral well completions. In many instances, the prior art liner hangers consist of a plurality of gripping slips radially disposed about the circumference of the liner. These slips of the liner hangers, while in a retracted position are fully, or at least partially exposed, thereby making them susceptible to either premature deployment against the sides of the casing, particularly by catching on a lateral wellbore casing window at the juncture between the main and lateral wellbores.
Multilateral drilling operations may include either providing a critical section of casing with a pre-formed window or forming a window in the casing after the casing is set in the main wellbore. The presence of the window presents potential problems for the exposed slips that were not present in conventional single wellbore operations. For example, in some instances, the portion of the liner on which the liner hangers are positioned is inadvertently inserted through the window. The window typically has sharp corners that can catch one of the exposed slips as the liner is inserted therethrough, causing it and the other slips to deploy prematurely. When the slips deploy in this manner, they hang on the corners of the window. Extensive and costly time and effort must then be spent in trying to free the liner. In some cases, the liner cannot be freed and a new lateral wellbore must be drilled, thereby greatly increasing the cost of the drilling project.
Another disadvantage associated with these conventional liner hangers is that the single set of liner hangers inadequately centralizes the portion of the liner that resides in the main wellbore for two reasons. First, lateral wellbores typically have significant curvature or "build radius" associated with their drill path. When the liner is inserted in the lateral wellbore with an upper portion remaining in the main wellbore, the curvature of the lateral wellbore path causes a spring force to be exerted by the liner's upper portion against the casing wall. The above-discussed conventional liner hangers, when deployed, have a slip arm that deploys the slip between the liner and the casing wall. However, when the slip arm encounters substantial resistant force resulting from wedging the slip between the confined space between the casing wall and the liner, the slip arm begins to bow or flex, and in some cases collapses completely, thereby preventing the slip from being deployed further to effectively centralize the liner's upper portion within the casing. Second, such conventional liner hangers typically have only one set of liner hangers positioned on the liner. Even with the hangers properly deployed, the section of liner below the hangers may still be de-centralized and therefore slightly curved because there is not another set of hangers to straighten and align a portion of the liner. When more than one liner hanger is employed, they must be sufficiently distanced, one from the others, so that the liner hanger is concentrically oriented to and parallel to the wellbore. A dual coned hanger is known that provides two points of centralization, but the two points are too close together to brace the liner sufficiently to maintain a concentric and parallel orientation during use.
Therefore, what is needed in the art is a liner hanger apparatus and methods associated therewith related to multi-lateral well drilling and completion processes that have a protective covering over the slip housing to prevent the slips from catching and deploying prematurely and that also provide for a centralization and forced alignment of a portion of the liner residing in the main wellbore that can act as a drill guide for subsequent drilling and completion operations.